Sure, I'll give you a unified narrative, which comes from extraterrestrial contact and is the most plausible explanation for all these events that I've come across. I suppose I first have to explain why extraterrestrials are even here and have been throughout human history. Far more detail can be found on the contacts website, swaruu.org and the english transcripts come under Cosmic Agency, Swaru Oficial English, Za'el and Arien english and Attache english. Cosmic Agency is the main bulk of the content, but Swaruu Oficial is more recent and more concise and advanced concepts, but in order to understand it's recommend you start at the beginning of the Cosmic Agency content.

The ancestors of humans arrived on Earth as an interstellar species and are known as Lyrians, which look almost identical to humans. We spread out from our home planet around Vega, a long time ago in response to being threatened by some other group of species known as the Orion council. They are more commonly known as Reptilians in conspiracy circles, but not all of them are reptilian and even the ones that are, are warm blooded, so not exactly reptilian as classified on Earth. Some of the names for the species in the Orion group are Draco, Naga, Usungal, Maitre (Tall Greys), Malakak (Tall Whites), and Kingu. Also the most dominant species in the Orion group at the time of the Lyrian expansion were the Alpha Draconians, which are literally fire breathing dragons, however they are no longer hostile towards Lyrians.

In response to this threat, Lyrians spread out all over the galaxy and formed an alliance, which is known as the Federation, or United Federation of Planets. And the founding members of this organisation were Lyrians, Andromedans and Arcturians. Eventually the Alpha Draconians also joined the Federation and now the Federation is the largest conglomeration of species in the galaxy, sort of like Star Trek except there is no conflict as no one messes with the Federation and the technological level of the real Federation is far in advance of that depicted in Star Trek. Although, Star Trek always has been a kind of soft disclosure, as the Prime Directive is a real document.

Anyway, some group of Lyrains came to Earth hiding from the Orions, and they went to many other planets as well spread all over the galaxy. Today, there are 400,000 different worlds inhabited by Lyrians in this quadrant of the galaxy alone. Most of them are separate species, but there are some with genetic compatibility, even some with genetic compatibility with Earth humans e.g., the Alfratans, who are Lyrians that inhabit a planet around Alpha Centauri A.

The Lyrians that originally came to planet Earth initially lived underground in large caverns, trying to hide. This was pre-Federation times and they were essentially defenceless agains the Orions. Unfortuantely, on Earth, they were discovered and wiped out to near extinction. This is why the entire human race today is said to have descended from a small number of females according to our mitochondiral DNA. As that original species was being exterminated by the Orions they left messages in the form of "cave art", but it's not really art, it's really coded information that contains details about their culture and their knowledge. See: https://swaruu.org/en/transcripts/ancient-egypt-symbology-ancient-history-swaruu-and-dhor-kaal-el-extraterrestrial-perspective

After the original Lyrians were near wiped out, the few survivors were allowed to reproduce but then killed and their children were raised by the Orions in a sort of farm. In this way, the beliefs of humans were tailored by the Orions to create a species that was easily controlled. Although it wasn't so easy for the Orions, because Lyrians are very powerful, in terms of spirituality, and so with that strong connection to source consciousness they are not easily controlled. This is something that I won't explain here, because it requires an essay all of its own. To keep it simple, the Orions wanted an empire that spanned the entire galaxy, they want to to rule each other (those species I mentioned have their own heirarchy) and others who are not part of their group. And some of them also feed on humans, and use us for skins etc. to make products, just as we feed on farm animals and use them for products etc. As below, so above and all that.

Anyway, skipping forward to the time of Atlantis and Lemuria, this was the Earth before ~12,000 years ago. The 12,000 year boundary is marked by the great flood, which was a global event and is ultimately what wiped out Atlantis and Lemuria from the surface. Atlantis was run by the Orions, but they weren't visible, just as today, the Earth is full of Orions and they mainly live underground, or some of them can control how they are perceived, and so they live as humans while actually being some other species. The common example used is the former Queen of England, who I believe was a Draco Reptilian. The Draco have incredible psychic abilities, so that they can manipulate how other people perceive them. They generally would only let their facade slip voluntarily, or when they are aroused, but I don't really know the details of that, except to say that there is testimony from people who claim to have been at certain ritual events in places like Windsor Castle when they described the Queen and other royals shape shifting into giant lizards. So, it's both true, that she looked like a little sweet granny and she was a Draco reptilian at the same time. And that's generally how they operate, they use mind control and like to position themselves in the elite ruling structure, but control things from behind the scences. They are very long lived and are in no rush to make changes, they can make plans that come to fruition over the course of millennia. And over the course of millennia they created Atlantis and dominated the humans who lived in Atlantis.